1. Field of the Invention
The present invention relates to a method of processing a substrate, and more particularly, a method of depositing a thin film made of a metal, such as tungsten, copper, nitride-titanium, titanium and the like, onto a substrate by CVD and of removing afterwards undesired parts of the thin film deposited on the back surface or the peripheral-edge side of the substrate, and further an apparatus suitable for carrying out the foregoing method.
2. Description of the Related Art
In manufacturing semiconductor devices on a substrate (or a wafer), recently, electronic circuit elements such as active elements and the like incorporated in the devices are more and more integrated and miniaturized. As a result, in a metallization process being one of the processes for manufacturing the semiconductor devices, thin film deposition based on a CVD (Chemical Vapor Deposition) method suitable for integration and miniaturization is being used instead of thin film deposition based on the conventional sputtering method.
On the other hand, conventionally, the thin film deposition was carried out to an entire front surface of the substrate to be processed in order to increase the amount of semiconductor-device chips yielded from a single substrate. However, when carrying out the thin film deposition onto the entire front surface of the substrate by using the CVD method in the metallization process as mentioned above, the thin film deposition causes a problem such that the thin films build up on the peripheral-edge side of the substrate and the back surface close to the peripheral edge.
Furthermore, in case of uniformly removing unnecessary or undesired thin films being parts of the thin film which is deposited onto the substrate, so far an etching-back method has been generally used, while a CMP (Chemical Mechanical Polishing) method corresponding to the advanced integration came in use in recent years. The CMP method, however, cannot be used for removing the thin film deposited on the peripheral-edge side of the substrate. Consequently, the thin films deposited on the peripheral-edge side naturally peel off in sequential processes and therefore cause generation of contamination particles which results in a drop in a yield. Then, in case of using the above-mentioned CMP method, the other techniques for removing the thin films deposited on the peripheral-edge side of the substrate is strongly required in order to decrease the generation of the contamination particles.
A typical conventional technique for removing the thin film deposited on the peripheral-edge side of the substrate is conceptually explained by referring to FIG. 5. This conventional technique relates to a CVD apparatus used for depositing a thin film made of e.g. a blanket tungsten on the entire front surface of the substrate.
A gas supply section 52 with a gas supply plate 53 is arranged at an upward position in a reactor 51, and the gas supply plate 53 has a plurality of projecting sections 61 at predetermined positions in a lower surface of the plate 53, which project in vertical direction. A bottom shape of the gas supply plate 53 is circular, for example, and in the plate 53 a plurality of gas inlets are formed in the region between a center and a peripheral section in a suitable arrangement. The plurality of projecting sections are arranged in a circle in the lower surface at a constant interval. The diameter of the circle on which the projecting sections are placed is slightly smaller than the diameter of the substrate. A substrate holder 54 whose upper surface is opposite to the gas supply plate 53 is placed in the inside region of the reactor 51. The upper surface of the substrate holder 54 is used as a substrate loaded surface with an almost circular shape. The substrate holder 54 has a heating device 55 in its inside and further receives a radio frequency (rf) power supplied by a radio frequency power supplying device 59. A reference number 55a designates an electric power generator for supplying power to the heating device 55.
A substrate 58 with a disk shape is placed on the upper surface of the substrate holder 54 and afterwards a thin-film deposition process is started. In the thin-film deposition process, a process gas is supplied into the reactor 51 from the gas supply section 52 and a tungsten thin film can be deposited on an entire front surface of the substrate 58 by the CVD method. On this occasion of the thin film deposition, the thin film can be naturally deposited on the peripheral-edge side of the substrate 58, and furthermore, on the back surface thereof.
Then, a process for removing the tungsten thin films stuck to the peripheral-edge side and the back surface of the substrate 58 follows. In this removal process, the substrate is processed in the reactor of the conventional apparatus, as described below. That is, in brief, the substrate 58 can be etched by radicals generated in the plasma.
Rods 60 for pushing up the substrate 58 lift it from the substrate holder 54, and the peripheral edge in front of the substrate 58 is pressed to the projecting sections 61 of the gas supply plate 53. The rods 60 are called "push-up rods" hereinafter. The push-up rods 60 can be activated by a substrate push-up rod driver 62. Further, the push-up rods 60 are arranged to pass the substrate holder 54, and electrically insulated from the substrate holder 54.
Next, the gas supply section 52 introduces an etching gas into a space between the gas supply plate 53 and the front surface of the substrate 58. There are clearances between the front surface of the substrate 58 and the gas supply plate 53 with the exception of the places where the projecting sections 61 exist. The etching gas introduced into the space between the substrate 58 and the gas supply plate 53 flows into the interior space of the reactor 51 through the clearances, and is evacuated afterwards to the outs ide through an evacuation section 56.
Next, the rf power is applied to the substrate holder 54 by the rf power supply device 59, and thereby, plasma can be generated in both spaces between the back surface of the substrate 58 and the substrate holder 54 and between the gas supply section 52 and the substrate holder 54. The radicals generated by the plasma, which can reach the substrate 58, remove the tungsten thin films deposited on the back surface and peripheral-edge side of the substrate.
The substrate 58 pressed against the projecting sections 61 in contact electrically with each other is kept to have an electrical potential equal to that of the gas supply plate 53, that is, an earth potential. Accordingly, even if the rf power is applied to the substrate holder 54, the plasma is not generated in the space between the substrate 58 and the gas supply plate 53. However, if there is electrically imperfect contact between the substrate 58 and the gas supply plate 53, the electrically imperfect contact causes a potential difference between them, and the plasma may be generated in the space formed between them. Therefore, the generation of the plasma between the substrate 58 and the gas supply plate 53 is more restrained by keeping the distance between the substrate 58 and the gas supply plate 53 smaller than the predetermined distance which makes the plasma generation difficult.
In the above-mentioned conventional arts, the rf power is applied to the substrate holder 54, while the gas supply section 52 is grounded. Conversely, the rf power may be applied to the gas supply section 52, while the substrate 58 may be grounded.
As other similar conventional arts, there are Tokko-Hei 6-70273 (Tokkai-Hei 3-97869; this reference corresponds to U.S. Pat. No. 5,075,256) and U.S. Pat. No. 4,962,049, for example. In the apparatus according to Tokko-Hei 6-70273 (Tokkai-Hei 3-97869), the substrate (wafer) on which the thin film has been deposited is placed so as to be in contact with the projecting sections formed on the lower surface of the face plate as a gas supply plate, and the process gas (etching gas) is supplied from the face plate in order to remove the films deposited on the backside and edge side of the substrate. Further, U.S. Pat. No. 4,962,049 shows the configuration that the semiconductor wafer is supported by the pins at the upper position above the conductive cathode at predetermined intervals, and the back surface of the wafer is processed by the plasma.
In the conventional apparatus firstly explained by referring to FIG. 5, the plasma used for the etching process in the reactor 51 can be generated in a region close to the peripheral edge of the substrate 58 and between the gas supply plate 53 and the substrate holder 54. In addition, there is the possibility that the plasma flows into the region near to the peripheral edge of the front surface of the substrate 58 through the clearances formed between the substrate 58 and the gas supply plate 53. Therefore, it causes a problem that most of the radicals produced by the plasma diffuse and enter into the space above the front surface of the substrate 58, and the tungsten thin film deposited on the front surface of the substrate is removed.
Further, since the substrate surface onto which the tungsten thin film is deposited is pressed to the projection sections 61, an easy to peel-off thin film such as the tungsten thin film e.g. causes contamination particles which produces a yield drop.